Various pyrazolone derivatives are known as a magenta dye forming coupler (hereinafter referred to as a magenta coupler). However, pyrazolone derivatives generally used for photographic light-sensitive materials are 4-equivalent couplers. Such compounds theoretically require the development of 4 moles of silver halide for forming 1 mole of a dye by reacting with an aromatic primary amine developing agent. On the contrary, pyrazolones having an active methylene group substituted by a group which can be released by oxidative coupling with an oxidation product of the primary amine developing agent require development of only two moles of silver halide. In addition, the 4-equivalent pyrazolone derivatives have a low color forming efficiency (conversion of the coupler into the dye) and form generally only a 1/2 mole or so of the dye per mole of the coupler.
As a means for improving the color forming efficiency by decreasing the amount of silver halide required for development, utilization of 2-equivalent pyrazolone magenta couplers has been proposed. Examples of pyrazolone derivatives which release an oxygen atom include compounds having an aryloxy group in the 4-position of 5-pyrazolone as described in U.S. Pat. No. 3,419,391 and compounds having an acyloxy group as described in U.S. Pat. Nos. 3,311,476 and 3,926,631.
Examples of pyrazolone derivatives which release a nitrogen atom include compounds having an imidazolyl group, a pyrazolyl group or a triazolyl group in the 4-position of 5-pyrazolone as described in U.S. Pat. Nos. 4,076,533 and 4,241,168.
Further, examples of pyrazolone derivatives which release a sulfur atom include compounds having a heterocyclic thio group or an arylthio group in the 4-position of 5-pyrazolone as described in U.S. Pat. No. 3,227,554, compounds having a thiocyano group in the 4-position of 5-pyrazolone as described in U.S. Pat. No. 3,214,437 and compounds having a dithiocarbamate group in the 4-position of 5-pyrazolone as described in U.S. Pat. No. 4,032,346. These compounds are advantageous in that most of them can be synthesized from 4-equivalent pyrazolones by one step. Also, these compounds are advantageous in view of photographic sensitivity and equivalency. It has been found that compounds having a 2-alkoxyarylthio group in the 4-position of 5-pyrazolone have exceptionally superior properties among couplers of type which release an arylthio group. More specifically, these compounds are described in U.S. Pat. No. 4,351,897. In addition, magenta color images formed from the couplers having a 2-alkoxyarylthio group have good fastness to light, while the light fastness of magenta color images formed from conventional couplers having an arylthio group is remarkably inferior.
However, with these 2-equivalent magenta couplers, a disadvantageous property whereby stains (increase in color density in unexposed areas) are formed by development processing is eliminated to a certain extent but the elimination is still insufficient.
The stains occurring in unexposed areas of silver halide color photographic light-sensitive material are undesirable since they are the definite factor in determining whether the whiteness of the non-image areas is good or bad. Further, the stains adversely affect the color turbidity of the images and injure their visual sharpness. Particularly, in case of reflective photographic materials, for example, photographic color papers, the reflective density of the stains is theoretically emphasized so that it becomes several times as high as the transmission density. Therefore, the stains are very important factors since a slight degree of stain can injure image quality.
The stains in the silver halide color photographic light-sensitive materials are roughly classified to four groups depending on the cause of the stain occurrence. First is a stain which is formed after the production of the photographic light-sensitive material and before the processing thereof due to heat or humidity. Second is a stain due to a development fog of silver halide. Third is a stain based on color contamination due to color couplers in a development processing solution (for example, aerial fog, etc.) or a stain due to a dye formed by the reaction with coupler of an oxidized developing agent which is formed by oxidation of a developing agent remaining in the silver halide emulsion layer by a bleach solution or oxygen in the air, etc., (for example, bleaching stain, etc.). And fourth is a stain based on changes in photographic materials after development processing with the passage of time due to light, humidity or heat. The stains due to the development processing of the photographic materials containing 2-equivalent magenta couples according to the present invention relate to the third and fourth stains described above.
A more difficult problem is that it is unusual to newly prepare a solution for the development processing before every development processing. In practice, the solution is employed by replenishing a developing solution in an amount depending on an amount of photographic materials developed. However, a composition of the solution cannot be maintained only by the replenishment of the components which are consumed by development.
In general, a solution for development processing includes a color developing solution, a stopping solution, a bleaching solution, a fixing solution or a bleach-fixing (blixing) solution, etc. Since the processing temperature is maintained at a high temperature such as from 31.degree. C. to 43.degree. C., the compositions of the processing solutions are changed by several factors such that the developing agent, etc., is subjected to decomposition for a long period of time or to oxidation when brought in contact with the air, that the components contained in the photographic light-sensitive materials are dissolved out and accumulated in the solution during the processing of the photographic light-sensitive materials, and that a processing solution is taken into the following bath by attaching with the photographic material. Thus, the processing solution becomes the so-called running solution. To eliminate such problems, a replenishment procedure in which chemicals lacked are supplementarily added to the solution and a regeneration procedure in which desirable components are removed are carried out. However, such procedures are still incomplete.
The photographic light-sensitive materials containing 2-equivalent magenta couplers have a large tendency to form stains in the running solution. However, the occurrence of such stains cannot be prevented by techniques heretofore known. A known method for preventing such stains involves the incorporation of a reducing agent, particularly, an alkylhydroquinone (for example, those as described in U.S. Pat. Nos. 3,935,016 and 3,960,570) into a photographic light-sensitive material, particularly, an emulsion layer wherein the stains are formed is effective. It is also known that a chroman, a coumaran (for example, those as described in U.S. Pat. No. 2,360,292), a phenol type compound (for example, those as described in Japanese Patent Application (OPI) No. 9949/76 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application")), etc., are effective. Furthermore, a sulfinic acid type polymer is known as being effective as described in U.S. Pat. No. 4,352,873. However, these known techniques cannot provide sufficiently good effects against the processing stain due to 2-equivalent magenta couplers, in particular, the processing stain owing to the exhausted solution, while a little effect is recognized.